1. Field of the Invention
The present invention broadly pertains to an appliance used in orthodontic treatment. More particularly, this invention pertains to a ceramic orthodontic appliance that includes a clip for releasably retaining an archwire in an archwire slot of the appliance.
2. Description of the Related Art
Orthodontic therapy is a specialized type of treatment within the field of dentistry associated with the supervision, guidance and correction of malpositioned teeth into proper locations. Orthodontic treatment can be useful in correcting defects in a patient's bite (also called occlusion) along with promoting better hygiene and improving the overall aesthetics of the teeth.
Orthodontic treatment often involves the use of tiny slotted appliances known as brackets, which are generally affixed to the patient's anterior, cuspid, and bicuspid teeth. After the brackets have been placed on the teeth, an archwire is received into the slot of each bracket and acts as a track to guide the movement of respective teeth to orthodontically correct positions. End sections of the archwire are typically captured in appliances known as buccal tubes that are affixed to the patient's molar teeth. After installation in the patient's mouth, the brackets, archwires, and buccal tubes are typically referred to collectively as “braces”.
Conventional brackets use an elastomeric ligature or metal ligature wire to secure the archwire in the slot of each bracket. However, there are also appliances known as “self-ligating” brackets, which do not require the use of ligatures. Instead of using a ligature, a self-ligating bracket uses a latch for securing the archwire in place. These types of brackets can be advantageous because levels of sliding resistance between the archwire and the bracket can be reduced, resulting in faster leveling and aligning of teeth. Moreover, the elimination of ligatures can simplify installation and removal of archwires during treatment, improve patient hygiene, and avoid the inconvenience of replacing elastomeric ligatures as a result of ligature staining.
Latches used in self-ligating brackets come in many shapes and sizes, and may comprise a clip, spring member, cover, shutter, bail, or other structure that is coupled to the bracket body and capable of releasably retaining an archwire in the archwire slot. As an example, a bracket used in the SMARTCLIP brand Self-Ligating Appliance System sold by 3M Unitek (Monrovia, Calif.) uses a latch based on two “C”-shaped clips comprising a shape-memory alloy that are coupled to the bracket body. The clips flex open and closed to receive and retain an archwire in response to a clinician applying suitable forces on the archwire. Examples of latches are also described in U.S. Pat. Nos. 6,302,688, 6,325,622, 6,582,226, 6,984,127, as well as in published U.S. patent application No. 2006/0172249. Aesthetic self-ligating bracket systems made from ceramics or other translucent materials are also possible.
In much the same way that a ligature secures the archwire on both the mesial (i.e. facing towards the center of the patient's dental arch) and distal (i.e. facing away from the center of the dental arch) sides of the bracket, the two clips of the SMARTCLIP brand self-ligating brackets mentioned above are symmetrically disposed on the respective mesial and distal sides of the archwire slot. This latch configuration, however, poses challenges for ceramic self-ligating brackets, which tend to be slightly larger than their metal counterparts. Specifically, problems may arise when bonding brackets to small teeth such as lower anteriors. Because lower anterior teeth are small, collisions (or interferences) can occur between adjacent brackets during bonding and prevent brackets from being located optimally on the tooth. Even in cases where the teeth are sufficiently large, bracket interferences may still occur if teeth are overlapping or have facial (i.e. towards the patient's cheek or lips) surfaces that are angled toward each other. Because lower anterior teeth are often crooked and induce these interferences, the clinician is frequently unable to successfully bond all the brackets on the first appointment and postpones bonding one or two brackets until such time that sufficient space has been created. This in turn extends treatment time and reduces the efficiency of treatment.
Rather than delaying the bonding of brackets, the clinician may choose instead to avoid interferences by bonding some brackets in locations other than their ideal locations. However, this too is disadvantageous because these same brackets will often need to be debonded and re-positioned later in treatment. Bracket re-positioning is not ideal because it requires an additional time investment by the clinician and another potentially uncomfortable procedure for the patient.
As can be appreciated, there is a need for a ceramic bracket that provides the advantages of a self-ligating bracket while minimizing interferences with adjacent brackets.